Method and device of melting together fiber ends

ABSTRACT

In a method of melting together axial ends of bunched fibers of thermoplastic material, the fiber ends are brought into contact with the heated surface of a stamp. The body of the stamp is heated by controlling an electric current passing through it. In one embodiment the stamp is cooled by a flow of compressed air before the stamp is separated from the fiber ends. In another embodiment, the stamp is separated from the melted fiber ends, heated to a higher temperature to vaporize any residual fiber material, and cooled by exposure to compressed air until it has no more than the temperature for melting the fiber material.

FIELD OF THE INVENTION

[0001] The invention relates to a method of melting together the axialends of bunched fibers of thermoplastic material, wherein the fiber endsare brought into contact with a heated surface of a stamp. The inventionrelates further to a device for attaching tufts of bristles for use inbrushes to carrier plates of thermoplastic material. The carrier plateswith the tufts of bristles attached thereto are incorporated in brushbodies, in particular for the fabrication of tooth brushes.

BACKGROUND OF THE INVENTION

[0002] Several methods are known for the fabrication of brushes. Inprinciple, brush bodies, having an array of holes corresponding to thedesired array of bristles, can be provided. The tufts of bristles arethen inserted into the holes of the brush body and anchored therein. Theanchorage of the tufts of bristles in the brush body by means of anchorplatelets or loops requires, however, highly performant and henceexpensive machines.

[0003] According to an alternative fabrication method for brushes, thetufts of bristles are attached to a carrier plate that then is builtinto a brush body. The carrier plate can be joined to the brush body byinjection-moulding around it or by welding. The carrier plate will beprovided with holes according to the desired hole pattern, theutilization ends of the tufts of bristles projecting out of one surfaceof the carrier plate, and the axial ends of the tufts of bristles to beanchored in the brush protruding slightly out of the opposite side. Aheated stamp is pressed against those ends of the tufts of bristles thatare to be anchored in the brush body, melting together the ends of thetufts of bristles and possibly deforming them into knobs. During thesubsequent separation of the stamp from the melted fiber ends, stickythreads and smearing of the viscous melted synthetic material may occur.Since, furthermore, the ends of the bristles as well as the carrierplate are heated, it is difficult on the one hand to effect thedeformation of the bristles necessary for a perfect anchoring, and toprevent on the other hand an unwanted deformation of the carrier plate,all the more since the carrier plate and the bristles usually are madeof different synthetic materials.

BRIEF SUMMARY OF THE INVENTION

[0004] The invention provides a method of melting together the axialends of bunched fibers of thermoplastic material, wherein the fiber endsare brought into contact with the heated surface of a stamp. Accordingto the invention, the body of the stamp is heated by passing acontrolled electric current through it, enabling extremely rapid andprecisely controllable temperature changes of the stamp.

[0005] In a first variant of the invention, the fiber ends are broughtinto contact with a heated surface of a stamp, which then is cooledabruptly. Only after cooling of the surface has occured, the fiber endsare separated from it. In this way, the melted fiber ends can be removedcleanly from the heated surface and show an overall shape that isdetermined by the geometry of the surface. In this variant theapplication of a non-stick coating is advantageous.

[0006] Like in the first variant, in a second variant according to theinvention the fiber ends are first brought into contact with a surfaceheated to a first temperature. The surface is then separated from thefiber ends while maintaining, however, the temperature of the surface.After that, the surface is heated up to a second, higher temperature inorder to vaporize any remainder of the fiber material adhering to thesurface. In a final step according to the method, the surface is cooledagain to the first temperature. In this variant, the adherenceproperties of the heated surface with respect to the heated fibermaterial are uncritical, a non-stick coating being hence unnecessary.

[0007] Both variants of the invention are especially suited for thefabrication of arrays of bristles to fabricate brushes. Fibers for thefabrication of brushes mostly consist of a thermoplastic material likepolyamide (“nylon”). This material can be deformed easily with theinventive method.

[0008] The invention further provides a device for attaching tufts ofbristles to carrier plates in order to manufacture brushes, enabling acontrollable and well reproducible operation of the stamp upon the endsof the bristles, assuring the desired deformation of the ends of thebristles without any unwanted deformation of the carrier plate. In thedevice according to the invention, the stamp is heated by an electriccurrent and can be cooled by a flowing cooling agent. The stamp can beheated rapidly and in a specific way by an electric current, especiallyif, according to the preferred embodiment, it has a low heat capacity,so that it quickly can be cycled through different temperature phases,including cooling by the cooling agent. Since the ends of the bristlesare heated only a very short time and instantanously cooled againafterwards, a smearing of the heated bristle material on the carrierplate is avoided. By the same token, the stamp may alternatively beheated to a second, higher temperature after having been withdrawn fromthe fiber ends in order to vaporize any remainder of the fiber materialadhering to the surface. The carrier plate itself is warmed up onlyslightly since the stamp is heated only for a short time to thetemperature needed to melt together the ends of the bristles, and isremoved or cooled instantaneously thereafter. Controlling the electriccurrent, particularly via pulse width modulation, allows a good controlof the intensity and the duration of the heating process.

[0009] Preferably, the stamp comprises a body of electrically conductingmaterial, on which two electrical high-current terminals in the shape ofbent-off contact shoes are formed. The body of the stamp has athin-walled stamp plate that may be strengthened by an angled borderingstrip. Suitable materials for the manufacturing of the stamp are metals,having on the one hand sufficent mechanical strength in order to assurethe desired low heat capacity needed for a fast change of temperature,and showing on the other hand only a moderate resistivity, so that onlyan uncritical electric voltage is needed to achieve the electricalheating power. Although, in this case, the required heating currentshave values of some hundred Amperes and more, for example 200 Amperes ata voltage of 7 V, such high currents can well be controlled usingavailable semiconductor components. In view of these criteria, stainlesssteel, titanium and NiCr-containing alloys are suitable materials forthe fabrication of the stamp.

[0010] In order to cool the stamp, compressed air is preferably used.Due to the low heat capacity of the stamp, only a short time is neededto cool it down by directing compressed air against it, so that cycletimes of about one second are feasable.

[0011] In the preferred embodiment of the device, a stamp carrier plateis provided with a plurality of stamps forming a group, and the samenumber of carrier plates is inserted into the corresponding openings ofa supporting plate opposite the stamps. Preferably, the stamps areelectrically connected in series at the stamp carrier plate, so that theintensity of the heating current does not increase. This measure isexpedient especially if the stamp carrier plate together with the stampsis reciprocated with respect to the carrier plates incorporated in thesupporting plate, in which case the electrical leads for the heatingcurrent have to be moved accordingly. As a consequence, large conductorcross-sections would be disadvantageous.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Further features and advantages of the invention will becomeapparent from the following description and from the accompanyingdrawings to which reference is made. The drawings show:

[0013] FIGS. 1 to 4 diagrams illustrating a first variant of the methodaccording to the invention;

[0014]FIG. 5 a schematic perspective view of the device;

[0015]FIG. 6 an enlarged sectional view of a part of the device;

[0016]FIG. 7 an enlarged perspective view of a part of the device;

[0017]FIG. 8 a perspective view in detail of a stamp of the device;

[0018]FIG. 9 a sectional view, showing a variant of the embodiment shownin FIG. 2;

[0019]FIG. 10 a partial section of another embodiment; and

[0020]FIG. 11 diagrams illustrating a second variant of the methodaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0021] In the first variant of the method, schematically depicted inFIGS. 1 to 4, fibers 1 of synthetic material are bunched, in particularby means of an apertured plate 2 for example, and set on a stop 3. Thestop 3 may be flat or comprise a shaped surface with a profile and canhence be applied in the known way to give the bristles an overallcontour by shifting them axially. The free fiber ends are situatedopposite a stamp 4 that has a solid body and can be heated by means ofan electric current passing through the body. The stamp 4 may have anyform, in particular one showing a shaped surface. The stamp 4 isthin-walled and has a low heat capacity. Hence, it can be heated veryrapidly using a resistance heating and cooled again equally rapidly withthe help of a flowing cooling agent.

[0022] In a first step the stamp 4 is heated to a temperature T₁. In asecond step the stamp 4 is pressed onto the fiber ends, as shown in FIG.1 and 2, melting together and shaping the fiber ends. In a third step,FIG. 3, the stamp 4 is then cooled quickly by compressed air directedagainst it. Only then, in a fourth step, the stamp is separated from thenow melted together and cleanly shaped fiber ends.

[0023] In the described embodiment of the device, it serves for thefabrication of tooth brushes, wherein a carrier plate, comprising tuftsof bristles, is inserted into a brush head and welded to it. Details ofsuch a device can be taken from the EP 0 972 464 A1 and the EP 0 972 465A1.

[0024] A mount 10 (FIG. 5) is provided with a stamp carrier plate 12that can be reciprocated vertically by means of guide rods 14, theactuation being assured by a pneumatic cylinder 16. To the bottom sideof the carrier plate 12 four support bases 18 are attached, carryingeach a heatable stamp 20 directed downwards. Below the carrier plate 12,spaced from and parallel to it, is provided a supporting plate 22 havingfour openings 24 opposite to the stamps 20. A carrier plate 26 made ofsynthetic material, comprising an array of holes corresponding to thedesired array of bristles, is insertable into each of these openings 24.

[0025] Via a compressed-air piping 28 branching at the stamp carrierplate 12, the device can be supplied with blasts of compressed airdirected against the stamps 20. Furthermore, two flexible high-currentcables 30, able to carry an electric current controlled by pulse widthmodulation, are connected to the stamp carrier plate 12.

[0026]FIG. 6 shows details of a single stamp of the device. This stamp20 whose structure is better understood from FIG. 5 consists of ametallic body, especially of stainless steel, with a thin-wall stampplate 20 a and two bent-off high-current terminals in the form ofright-angled contact shoes 20 b, 20 c formed thereon. These contactshoes 20 b, 20 c in addition serve the attachment of the stamp 20 to thesupport bases 18, which in turn are employed for electrically connectingthe four stamps 20. As can be seen from FIG. 6, the current cables 30are each directly connected to a cable shoe. The support bases 18 areprovided with openings 18 a being connected through the stamp carrierplate 12 to the compressed-air piping 28 and directing thecompressed-air flow against the stamp plate 20 a.

[0027] As further can be seen from FIG. 6, the carrier plate 26 isinserted into the opening 24 of the supporting plate 22 in such a waythat its circumferential border is held in place by the boundary of theopening 24. The tufts of bristles 32 inserted into the holes of thecarrier plate project 2 to 3 millimeters out of the side of the carrierplate 26 facing the stamp 20 and are propped at the opposite side at apush plate or stop 34. This stop can either be flat or comprise a shapedsurface that in addition can be used to give rise to a profile of thetufts of bristles by axially shifting the individual bristles within asingle tuft. The surface of the stamp 20 facing the carrier plate isprovided with sharp projections 36, whose tips point towards the area ofthe carrier plate surrounding the holes and hence the tufts of bristles.The surface of the stamp facing the carrier plate further is providedwith a non-stick coating.

[0028] As is apparent from FIG. 7, the four stamps 20 at the stampcarrier plate 12 are electrically connected in series. The connection ofthe stamps can be realised by individual cable sections or equally by anappropriate design of the support bases 18.

[0029] From the representation of the FIG. 8 it is apparent that thestamp is a thin-wall member that is given a high inherent stability bysuitable roundings, formed-on ledges, a bent-up circumferential borderand the angled structure of the contact shoes.

[0030] As further is apparent from FIG. 7, at least one of the stamps20, though preferredly each stamp, is associated with a temperatureprobe 40. The one or each of the temperature probes 40 is connected to acontroller 42 driving an electric current supply 44, to the outputterminals of which are connected the current cables 30. The currentsupply 44 preferably operates with pulse width modulation.

[0031] In a typical embodiment of the device, the body of each stamp 20is made of stainless steel. The wall thickness near the stamp plate 20 ais only a fraction of a millimeter. With a length of the stamp plate ofabout 20 millimeters and a width of about 10 millimeters, there resultsa heating power of about 1400 W, corresponding to a current of 200Amperes at 7 V. In this case, the body of the stamp has such a low heatcapacity that the heating/cooling-cycle achievable is of the order ofone second. The fast cooling is a consequence of the controlled blast ofcompressed air alone, being directed against the stamp plate.

[0032] In the embodiment shown in FIG. 9, in addition to the supportingplate 22 the carrier plate 26 is overlapped by a movable carrier ring48. The carrier ring 48 is provided with a through opening for thepassage of the stamp 20. The carrier ring 48 ameliorates the support atthe circumferential border of the carrier plate 26 to prevent it from adeformation effected by the heated stamp 20. With this embodiment of thedevice an excellent dimensional accuracy of the carrier plate 26 isassured, resulting in a clean joining with the brush head during thesubsequent welding.

[0033] In the embodiment shown in FIG. 10, the through holes areenlarged on the side of the fiber ends to be melted together, theenlargements being cone-shaped in particular. Pressing the heatedsurface of the stamp on the plasticized mass of the fiber ends meltedtogether, the mass is pressed into these enlargements resulting infrustum-shaped knobs at the melted fiber ends, that are referenced 5 inFIG. 10. Due to these knobs, the “pull-out force”, i.e. the tensileforce in the direction “A” in FIG. 10 at which a tuft releases from thecarrier plate 26 is increased strongly. An additional enhancement isachieved in that at least part of the plasticized mass is transformedinto a continuous layer by pressing the heated stamp onto it, asindicated at 6 in FIG. 10. To facilitate the inserting of the tufts offibers 1 into the through holes of the carrier plate 26, these throughholes are enlarged on the other side of the carrier plate 26 too, asindicated at 7 in FIG. 10.

[0034] The second variant of the method as depicted schematically inFIGS. 11 to 15 starts out from the same disposition as the first variantof the invention (FIGS. 1 to 4). Identical parts are indicated by thesame reference numerals.

[0035] The first two steps of the second variant of the methodcorrespond to the first two steps of the first variant. The stamp 4 isheated to a first temperatuer T₁, and pressed onto the fiber ends, asshown in FIGS. 11 and 12. In a third step the stamp 4 is now withdrawnfrom the fiber ends, keeping, however, its temperature constant (FIG.13). Occasionally, after having withdrawn the stamp 4 at the temperatureT₁, some material of the fibers still adheres to it. In order to removethis material, the stamp, in a fourth step, is heated to a second,higher temperature T₂ (FIG. 14) that is chosen such that in a pyrolysisprocess the material of the fibers first desintegrates into monomersbefore being vaporized. In this way, the stamp 4 is clean again and doesnot have any residual deposits. In the final step the stamp 4 is cooledto the temperature T₁ by directing compressed air against it (FIG. 15).Using fibers of polyamide, the temperature T₁ lies between 250° C. and300° C. and the temperature T₂ between 600° C. and 700° C.

1. A method of melting together axial ends of bunched fibers ofthermoplastic material, wherein said axial ends are brought into contactwith a heated surface of a stamp, heating of said stamp being caused bypassing a controlled electric current within the body of the stamp. 2.The method according to claim 1 , wherein said stamp is cooled rapidlyand the fiber ends are separated from the surface of the stamp onlyafter cooling of the surface has occured.
 3. The method according toclaim 2 , wherein the surface of the stamp is cooled by a flow of acooling agent.
 4. The method according to claim 1 , wherein the electriccurrent is controlled so that the stamp is heated alternately to a firsttemperature at which it is brought into contact with the fiber ends, andto a second, higher temperature at which fiber material adhering to thesurface of the stamp is vaporized.
 5. The method according to claim 1 ,wherein tufts of fibers for the fabrication of brushes are formed bymelting together fiber ends to be attached to the brush body.
 6. Themethod according to claim 5 , wherein a plurality of tuft ends aresimultaneously brought into contact with the surface of the stamp. 7.The method according to claim 6 , wherein the tufts are inserted intothrough holes of a carrier plate and attached to said carrier plate bymelting together adjacent tuft ends.
 8. The method according to claim 7, wherein the through holes are enlarged on a side of the carrier platewhere the tuft ends are melted together, and plasticized mass of fibermaterial is pressed into the enlargements of the through holes bypressing the heated surface of the stamp against the plasticized mass.9. The method according to claim 8 , wherein at least part of theplasticized mass is shaped into a continuous layer by pressing theheated surface of the stamp onto the mass.
 10. A device for attachingtufts of brush bristles to carrier plates of thermoplastic materialprovided with an array of holes corresponding to an array of brushbristles, comprising a heatable stamp that can be pressed onto ends ofthe tufts protruding on one side of the carrier plate out of said holes,said stamp having a body and a pair of terminals on opposed sides ofsaid body, and further comprising a controlled electric power supplyconnected to said terminals to pass a controlled electric currentthrough the body of said stamp.
 11. The device according to claim 10 ,wherein said a controlled flow of a cooling medium is selectivelydirected at the body of the stamp.
 12. The device according to claim 10, wherein the body of the stamp is made of an electrically conductingmaterial of a moderate resistivity.
 13. The device according to claim 12, wherein the body of the stamp comprises a thin-walled elongate stampplate with a pair of terminals formed on opposed ends of the stampplate.
 14. The device according to claim 13 , wherein the stamp plate isstrenghtened by a bent-off edge strip.
 15. The device according to claim13 , wherein said terminals are formed by a pair of bent-off contactshoes.
 16. The device according to claim 15 , wherein said contact shoescomprise support brackets for attachment of the stamp to a stamp holder.17. The device according to claim 10 , wherein said stamp has a surfacefacing the carrier plate and provided with projections that have tipsopposite to an area adjacent to and surrounding the holes of the carrierplate.
 18. The device according to claim 10 , wherein said stamp has asurface facing the carrier plate and provided with a non-stick coating.19. The device according to claim 10 , comprising a supporting platewith an opening, said carrier plate fitting into said opening of thesupporting plate.
 20. The device according to claim 19 , wherein amovable supporting ring with a through opening for the stamp is able tobe engaged around said carrier plate fitted into the opening of thesupporting plate.
 21. The device according to claim 11 , wherein saidcooling medium is formed by compressed air.
 22. The device according toany of the claim 10 , wherein a stamp carrier plate is provided with aplurality of stamps and a corresponding plurality of carrier plates areinsertable into corresponding openings of a supporting plate alignedwith said stamps.
 23. The device according to claim 22 , wherein saidstamp supporting plate can be reciprocated with respect to thesupporting plate.
 24. The device according to claim 22 , wherein thestamp carrier plate is provided with flow channels for the cooling agentopening opposite the stamps.
 25. The device according to claim 10 ,wherein the stamps are electrically connected in series.
 26. The deviceaccording to claim 12 , wherein the body of the stamp consists of ametal having a resistivity in a range defined by the resistivity ofstainless steel, titanium and NiCr-based alloys.
 27. The deviceaccording to claim 10 , wherein electric power is supplied to the stampin the form of high current pulses of some hundred Amperes at a voltageof a few volts.
 28. The device according to claim 10 , comprising atleast one temperature probe associated with the stamp, the electricpower supply being controlled according to the temperature measured bysaid probe.
 29. The device according to claim 28 , wherein said electricpower is controlled using pulse width modulation.